Soil nitrogen availability and transformations differ between the summer and the growing season in a California grassland

► We compare N dynamics in summer vs. growing season in California grassland soils. ► Nitrogen availability and net N mineralization are greater in summer. ► Nitrification and denitrification potentials are higher in summer. ► Microbial biomass is higher in the summer. ► A microbial-scale hydrological connectivity model may explain observed patterns.